The present invention relates to a novel developing solution for a photosensitive lithographic printing plate, a plate-making method of a lithographic printing plate, and a photosensitive lithographic printing plate. More specifically, the present invention relates to a developing solution optimal for a photopolymerizable lithographic printing plate which does not cause the reduction of developing properties with the lapse of time and repeated use, has good developing properties to a non-image domain (an unexposed domain) of a lithographic printing plate, prevents staining due to printing, gives less damage due to development to an image domain (an exposed domain), forms a stable image, does not cause printing troubles during printing such as blinding, and realizing high printing durability. The present invention further relates to a plate-making method of a lithographic printing plate and a photosensitive lithographic printing plate.
The developing solutions for photopolymerizable lithographic printing plates conventionally widely used are divided broadly into the following a) to c), i.e., a) a non-aqueous developing solution mainly comprising an organic solvent, b) an aqueous developing solution mainly comprising an inorganic alkali, and c) an aqueous developing solution mainly comprising an organic base.
Of the above three developing solutions, developing solutions b) and c) are used these days from the environmental demands.
Describing these two developing solutions in detail, a silicate is contained in the inorganic alkali developing solution b) near pH 12 for carrying out hydrophilizing treatment on a support generally after development.
A silicate is an essential component for performing hydrophilizing treatment, i.e., for preventing staining of a non-image domain at printing.
For example, the developing solution having pH of 12 or higher as disclosed in JP-A-8-248643 (the term xe2x80x9cJP-A xe2x80x9das used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and the developing solution having pH of 12 or lower as disclosed in JP-A-11-65129 are known as developing solution b). However, the former developing solution having pH of 12 or higher is liable to dissolve the aluminum used generally as a support, in particular when an image domain comprises minute dots, the aluminum support just under the image domain is dissolved by a side-etching phenomenon to cause the separation of minute dots from the support (dot-skipping) at printing, which extremely deteriorates a press life (i.e., a printing durability).
Further, a developing solution having pH of 12 or lower is preferred in the point of the above-described press life and the prevention of printing staining, but as a result of continuing development processing for a long period of time, pH is liable to lower due to the effect of, e.g., the carbon dioxide gas in the air, and the silicate precipitates in a developing solution at this time and development processing becomes unstable.
As an example of a developing solution, developing solutions not containing a silicate are disclosed in JP-A-61-109052, West German Patent 1,984,605, JP-A-2000-81711 and JP-A-11-65126, but all of these developing solutions are not only more disadvantageous than those containing a silicate in the point of the printing staining but the press life is also deteriorated.
On the other hand, as the organic base developing solution c), those containing an organic amine such as an ethanolamine and an alcohol-based organic solvent such as a benzyl alcohol as an auxiliary developing agent are known. The pH value of these developing solutions is certainly low, such as about 10, and so they are difficult to be affected by carbon dioxide gas and processing stability is good, but they are not only disadvantageous in the point of hydrophilization to a support, but also their osmotic power to an image domain is too high, thus there arises a problem that minute dots are separated from the support at development, i.e., an image-forming property is deteriorated.
That is, with respect to a photopolymerizable lithographic printing plate, a suitable developing solution is not found yet from the points of image-forming property, resistance to printing staining, printing durability and processing stability.
With respect to the composition of a developing solution, it is known that whether silicate is contained or not, whether pH is high or low, and the difference between an inorganic alkali and an organic alkali greatly influence a development phenomenon but conventional combinations cannot solve the above problems.
Further, when development processing of a photopolymerizable lithographic printing plate is continued for a long period of time, insoluble substance is accumulated, agglomerated, precipitated and becomes development scum, which becomes a main cause of making development processing unstable.
The components of such development scum have not been clearly known until now but it was found from the analysis that much of the scum was insoluble components of a developing solution contained in a photosensitive layer.
As the insoluble components, e.g., various kinds of colorants which are added to a photosensitive layer for the purpose of discriminating an exposed domain from an unexposed domain can be exemplified. In the case of photopolymerizable lithographic printing plates, for the purpose of avoiding desensitization due to radical supplement and desensitization due to unnecessary interaction (energy transfer and electron transfer) with an initiator system (an initiator alone, or combination of an initiator with a sensitizing dye), a pigment is used as the colorant which is not molecularly dispersed in a photosensitive layer but is dispersed as an aggregate with maintaining a crystalline state. However, these pigment are substantially insoluble in a developing solution, therefore they are at first temporarily dispersed in a developing solution in a development step for removing an unexposed area but when development processing is continued for a long period of time, they are accumulated, agglomerated, precipitated and come to development scum.
On the other hand, various photopolymerization initiators (radical generating agents) are used in a photopolymerizable lithographic printing plate to cope with laser light sources which are making progress in recent years. Of these initiators, titanocene-based initiators are known as the initiators which have photosensitivity in the wavelength of laser light source and excellent in stability and sensitivity. However, titanocene-based initiators are organic metals and insoluble in a developing solution similar to the above pigments, and temporarily dispersed in a developing solution but when development processing is continued for a long period of time, they are accumulated, agglomerated, precipitated and also come to development scum.
With respect to the processing stability, it is very important to solve not only the problem of the precipitation of silicate with the reduction of pH but also the problem of development scum.
That is, as the developing solution for a photopolymerizable lithographic printing plate, a developing solution which satisfies the above-described image-forming property, the compatibility of printing staining resistance with printing durability, and processing stability is desired.
Further, since conventionally broadly used negative type photosensitive lithographic printing plates are comprising a hydrophilized aluminum plate having provided thereon a diazo resin, the use of an organic solvent in a developing solution cannot be helped, hence there are fears of the disposal of developing waste solution and the influence to the environment.
Further, an orthoquinonediazide compound is used in combination with a novolak resin in a photosensitive layer of a positive type photosensitive lithographic printing plate, and an alkaline aqueous solution of silicate which can dissolve a novolak resin is used in a developing solution. However, the pH value capable of dissolving a novolak resin is 13 or so, and if a developing solution having such high pH is attached to the skin or a mucous membrane, it irritate the skin hard, hence sufficient care should be taken to handle it.
On the other hand, a photosensitive lithographic printing plate comprising an aluminum support having a photosensitive layer of a photopolymerizable photosensitive lithographic printing plate is also used and aqueous solutions of silicate, phosphate, carbonate and hydroxide of alkali metal and an organic amine compound are proposed as the developing solution.
For example, a developing solution having pH of 12 or more and containing silicic acid alkali salt and an amphoteric surfactant is disclosed in JP-A-8-248643, and a developing solution containing silicic acid alkali silicate defined by SiO2/M2O (M represents an alkali metal) having pH of 12 or less is disclosed in JP-A-11-65129.
The former has a problem that an image domain is liable to be damaged by development due to high pH value of the developing solution in addition to a problem of handling, and the latter has a problem that silicate gels and is insolubilized with the slight reduction of the pH value of the developing solution during use.
As developing solutions not containing silicic acid alkali salt, a developing solution comprising an alkali reagent, a complexing agent, an anionic surfactant, an emulsifying agent, an n-alkanoic acid, etc., is disclosed in JP-A-61-109052, and a developing solution comprising an alkali agent, a complexing agent, an anionic surfactant, an amyl alcohol, N-alkoxyamines, etc., is disclosed in West German Patent 1,984,605, but the damage to an image domain is great due to their high pH values and organic solvents contained, and sufficient printing properties, such as press life, cannot be obtained.
As a developing solution having relatively low pH (12 or less) and not containing silicic acid alkali, a developing solution comprising an aqueous solution of potassium hydroxide containing an anionic surfactant is disclosed in JP-A-2000-81711, and a developing solution comprising an aqueous solution of alkali metal carbonate having pH of from 8.5 to 11.5 is disclosed in JP-A-11-65126.
However, since these developing solutions having relatively low pH are fundamentally poor in dissolving power of photopolymerizable photosensitive layer, development does not progress sufficiently with a printing plate after the lapse of time, as a result the problem of residual film arises. For resolving these problems, it is necessary to contrive to increase the acid value of the high polymer binder in a photosensitive layer to thereby improve developing property, or use a monomer having an acid radical in combination. However, when such a binder having high acid value is used, printing troubles during printing, e.g., a trouble that ink comes to not adhere during printing (blinding), are liable to occur.
Accordingly, the objects of the present invention are to provide a developing solution for a photosensitive lithographic printing plate by which the above-described weak points of conventional techniques can be overcome, an image-forming property is not damaged, staining resistance during printing can be compatible with printing durability, the above-described insoluble compounds in a developing solution can be dissolved or dispersed stably for long time, and processing stability can be improved, and provide a plate-making method of a lithographic printing plate and a photosensitive lithographic printing plate.
A further object of the present invention is to provide a plate-making method of a lithographic printing plate using an alkali developing solution having comparatively low pH which is preferable in environment and safety, in which plate-making method can produce a lithographic printing plate having a preferred non-image domain stably having good developing property without staining due to printing, can give less damage by development to an image domain, can form a stable image without printing troubles during printing such as blinding, and can realize high printing durability.
As a result of eager investigation by the present inventors, the above objects of the present invention have been achieved by the following means.
That is, the embodiments of the present invention are as follows.
(1) A plate-making method of a lithographic printing plate which comprises the steps of exposure of a photosensitive lithographic printing plate having the acid value of a photosensitive layer of 1.0 meq/g or less with a laser beam, and then development with a developing solution having a pH of 13.0 or less at a developing speed in an unexposed domain of 0.05 xcexcm/s or more and at an osmotic speed of a developing solution in an exposed domain of 0.1 xcexcm/s or less.
(2) A plate-making method of a lithographic printing plate which comprises the steps of exposure of a photosensitive lithographic printing plate having the acid value of a photosensitive layer of 1.0 meq/g or less with a laser beam, and then development with a developing solution having a pH value of 13.0 or less so as to dissolve the photosensitive layer in order from the surface without swelling and peeling of the photosensitive layer.
(3) A developing solution for a photosensitive lithographic printing plate which is a non-silicate-based developing solution and contains an inorganic alkali agent and a nonionic compound represented by the following formula (I):
Axe2x80x94Wxe2x80x83xe2x80x83(I)
wherein A represents a hydrophobic organic group having 1.5 or more of logP of Axe2x80x94H, and W represents a hydrophilic organic group having less than 1.0 of logP of Wxe2x80x94H.
(4) The developing solution for a photosensitive lithographic printing plate as described in the above item (3), which contains a chelating agent to a divalent metal.
(5) The developing solution for a photosensitive lithographic printing plate as described in the above item (3),which has a pH of from 100.0 to 12.5 and electrical conductance of from 3 to 30 mS/cm.
(6) The developing solution for a photosensitive lithographic printing plate as described in the above item (3), which contains a carbonic acid or a carbonate.
(7) The plate-making method of a lithographic printing plate as described in the above item (1) or (2), wherein the photosensitive lithographic printing plate is a photopolymerizable lithographic printing plate having on a support a photopolymerizable photosensitive layer containing the following i) and ii) as essential components:
i) a compound having an addition polymerizable ethylenically unsaturated bond, and
ii) a photopolymerization initiator.
(8) The plate-making method of a lithographic printing plate as described in the above item (7), wherein the photopolymerizable photosensitive layer contains a titanocene-based initiator or a colorant (e.g., a pigment).
(9) The plate-making method of a lithographic printing plate as described in the above item (7), wherein the support is an anodized aluminum support containing an organic compound having a phosphorus-containing atomic group on the surface of the support.
(10) A photosensitive lithographic printing plate comprising a photopolymerizable photosensitive layer, wherein the photosensitive layer contains a compound having an acid radical having a pKa of 9 or less and the acid value of the photosensitive layer is from 0.20 to 0.60 meq/g.
(11) A plate-making method of a lithographic printing plate which comprises the steps of image exposure of a photosensitive lithographic printing plate comprising an aluminum support having an anodized film on the surface having provided thereon a photopolymerizable photosensitive layer containing a compound having an addition polymerizable ethylenically unsaturated double bond, a high polymer soluble or swelling in an alkaline aqueous solution, and a photopolymerization initiator with a laser beam, and then development with a developing solution comprising an alkaline aqueous solution containing at least one of a nonionic aromatic ether-based activator represented by the following formula (I-A) and a nonionic aromatic ether-based activator represented by the following formula (I-B): 
wherein R1 and R2 each represents H or an alkyl group having from 1 to 100 carbon atoms, and n and m each represents an integer of from 0 to 100.
(12) A plate-making method of a lithographic printing plate which comprises the steps of image exposure of a photosensitive lithographic printing plate comprising an aluminum support having provided thereon a photopolymerizable photosensitive layer containing a compound having an ethylenically unsaturated double bond, a photopolymerization initiator and a high polymer binder, and then development with a developing solution containing an inorganic alkali agent and a nonionic surfactant having a polyoxyalkylene ether group, having a pH of from 10.0 to 12.5, and an electrical conductance of from 3 to 30 mS/cm.
As a result of eager investigations of developing solution compositions, resistance to printing staining could be compatible with printing durability without impairing an image-forming property, the above-described insoluble compounds in a developing solution could be dissolved or dispersed stably for long time, and processing stability could be improved by using a developing solution comprising special components.
At present, the special developing solution is thought to be the developing solution composition which satisfies the following requisites.
First, to be capable of extraordinarily well functioning to image-forming property (the developing property at an unexposed domain is high, the osmotic property of a developing solution to an exposed domain is low, and dissolution behavior of a photosensitive layer is non-swelling and a photosensitive layer is dissolved in order from the surface).
Secondly, to be capable of excluding the unexposed domain of a photosensitive layer completely and reclaiming the support surface as a hydrophilic layer generating no printing staining.
Thirdly, for stably dispersing or solubilizing the above-described compounds insoluble in a developing solution, a nonionic compound represented by formula (I) having a hydrophilic site to be dispersed and stabilized with a hydrophobic site interacting with these insoluble compounds must be contained.
Fourthly, the concentration of salt must be low to prevent salting out and the reduction of a developing speed (the developing solution must be non-silicate-based and the pH must be low as compared with conventionally used alkali developing solutions).
Fifthly, to contain a chelating agent to remove a divalent metal such as a Ca ion contained in water which is an unstabilizing factor at development processing.
Of these, with respect to the first and second requisites, the characteristics of photosensitive layer components are also important factors. The photosensitive layer of a photopolymerizable lithographic printing plate is not restricted particularly, but until the present it is known that having lower photosensitive layer acid value than conventional acid value is thought to be important to obtain a synergistic effect with the developing solution according to the present invention.
The present inventors have found that, by combining an alkali solution having relatively low pH with a nonionic surfactant having special structure, and adjusting the salt concentration in the developing solution, the dissolving speed of the unexposed domain of a photopolymerizable photosensitive layer increases and, contrary to this, the osmosis of the developing solution is controlled in the area crosslinked by polymerization of the exposed domain, thus the present invention has been accomplished.
Therefore, a printing plate comprising an unexposed domain having no printing staining and an exposed domain having high press life (i.e., high printing durability) can be obtained stably according to the present invention.